Angles on a line and at a point: what children learn
In this game children use these facts to find missing angles on a straight line, around a point and in quarter turns. Every question needs one fact and one subtraction.
Supports part of Common Core 4.MD.C.7: angle measure is additive, so missing angles can be found by subtracting. This focused game does not cover the entire standard.
Common Core connection: 4.MD.C.7. This is focused practice for part of the standard.
How to play
Answer 10 questions before the clock runs out. Tap an answer, or press 1 to 4. Each game has 10 multiple-choice questions and a 150-second timer. A wrong answer shows the correct one before moving on. You earn up to three stars depending on your score.
Step by step
- Straight line: 180°. Angles on a straight line add up to 180°.
- Around a point: 360°. Angles all the way round a point add up to 360°.
- Right angle: 90°. Two angles that make a right angle add up to 90°.
- Subtract what you know. Take the known angles away from the total.
Worked examples
Example 1: Two angles sit on a straight line. One is 40°. What is the other?
Working: 180 − 40 = 140.
Answer: 140°
Example 2: Angles around a point: 100°, 120° and one more. What is the missing angle?
Working: 100 + 120 = 220. 360 − 220 = 140.
Answer: 140°
Example 3: Two angles make a right angle. One is 35°. What is the other?
Working: 90 − 35 = 55.
Answer: 55°
Common mistakes and how to fix them
- Using 360° for a straight line. Draw a straight line and a half circle above it: half a turn is 180°.
- Forgetting to add the known angles first. Add all the angles you know, then subtract from the total.
- Subtraction errors like 180 − 65 = 125. Count on from 65 to 70 (5), then to 180 (110): 115.
Activities to try at home
- Cut a paper circle into pieces and check that the angles add up to 360°.
- Make two angles on a straight line with a ruler and pencil and measure both.
- Ask: if I turn 90° and then 180°, how far have I turned?
Ideas for the classroom
- Students tear the corners off a paper shape and line them up on a straight line.
- Give missing-angle puzzles where students must explain which fact they used.
- Make 'angle families' that add up to 90°, 180° and 360°.
Free printable game and worksheet
The free printable starts with a game sheet, such as a color-by-answer picture, an answer maze or a secret-code joke, followed by a worksheet. Both use the same checked questions as the online game, and the answers are on the last page. Print it, or save it as a PDF from your browser’s print menu.
Open the free printable game and worksheet
Frequently asked questions
How should I choose this game for my learner?
Supports part of Common Core 4.MD.C.7: angle measure is additive, so missing angles can be found by subtracting. This focused game does not cover the entire standard.
Should children measure to check?
It helps at first, but the aim is to calculate. Diagrams are often not drawn to scale.
Can it be played with a keyboard?
Yes. Press 1, 2, 3 or 4 to choose an answer.